1. Field of the Invention
The present invention relates to generally rectangular or circular vent apparatus for protecting a confined space having a vent aperture for relief of a high overpressure condition. The vent apparatus is especially useful for covering relief openings in enclosures subject to rapid pressure build-ups such as may occur during explosions or uncontrolled combustion events in bag houses, duct work communicating with the bag houses, processing equipment, duct work leading to and from the processing equipment, buildings, pressure vessels, and other types of commercial and industrial installations where explosions or uncontrolled combustion events producing high overpressures may occur.
More particularly, the invention concerns vent apparatus of overall rectangular or generally circular configuration that will vent the confined space when an excessive overpressure of predetermined magnitude is exerted on the vent apparatus, and that will then reclose upon relief of the pressure to:                eliminate or reduce the ingress of air and thereby oxygen, thus mitigating the effects of a secondary explosion if the protected area remained exposed to the surrounding atmosphere via the vent opening;        prevent continuation of combustion of process materials that could cause permanent damage to the protected installation;        improve suppression of flames/fire, where inert gas, water mist, or the like, is used as an extinguishment agent, by virtue of the fact that the resulting combustion gases/flames cannot escape through venting holes; and        reduce/eliminate contamination of the protected process zone.        
The vent structure adapted to be mounted over a vent aperture of a confined space to be protected from a high overpressure condition includes a vent unit having a spring steel panel provided with a movable pressure relief portion defined by a line of weakness that will give way and allow the relief portion to open under a predetermined overpressure. As soon as the overpressure is relieved, the modulus of resilience and elasticity of the spring steel is sufficient to cause the pressure relief portion to return to its initial position, thereby closing the vent aperture. A backstop, which is either rectangular or circular depending upon the overall shape of the vent apparatus, extends outwardly from the vent and is provided for arresting movement of the relief portion of the spring steel panel to a selected opening position when a predetermined overpressure is applied against the relief portion of the vent unit of the vent structure, thereby preventing excessive bending of the relief portion when the vent unit of the vent structure experiences a high overpressure as the result of an explosion or other untoward pressure conditions. The backstop preferably has a curved surface adjacent to and outwardly of the relief portion of the vent unit, as well as a curved surface at the upper end thereof extending away from the main body of the backstop. The backstop is positioned to prevent the relief portion of the vent opening to an extent that the elastic limit of the spring steel metal is exceeded. Further, the two curved surfaces of the backstop function to progressively decrease, absorb, and dampen kinetic energy created by the rapidly moving relief portion during opening until kinetic energy is dissipated when movement of the relief portion of the vent is stopped by engagement of the backstop as opposed end segments thereof bend about respective spaced curved surfaces.
2. Description of the Prior Art
Explosion vents traditionally have been provided with a rupturable sheet of metal that has score lines or interrupted slits that define a line of weakness presenting the relief area of the vent. The amount of overpressure required to open the relief area of the vent is determined by, among other things, the type, thickness, and physical properties of the metal selected for fabrication of the explosion vent, the shape and nature of the line of weakness, the location of the line of weakness in the overall area of the vent, and oftentimes the provision of a series of spaced cross-tabs overlying the line of weakness in predetermined relative dispositions.
An exemplary explosion vent of this type is shown and described in U.S. Pat. No. 6,070,365, wherein a rectangular pressure relief panel is mounted in a frame adapted to be secured across a pressure relief opening. The unitary relief panel is formed from a single sheet of steel, stainless steel, Inconel, or other similar metal, and has a three-sided line of weakness defined by a plurality of interrupted slits. The series of spaced rupture tabs positioned over the line of weakness as shown in the '365 patent, must rupture before the relief area of the panel gives away under a predetermined high overpressure resulting from an explosion or a fast-burning fire.
U.S. Pat. No. 5,036,632 is another example of a conventional rectangular metal sheet explosion vent that has a three-sided line of weakness defined by interrupted slits. A layer of synthetic resin material or the like may be provided in covering relationship to the line of weakness slits. Rupturable tabs are also provided in the type of vent shown and described in the '632 patent that must break before the central section of the panel ruptures along the slit line to relieve an overpressure. An elastomeric sealing gasket or gaskets may be provided around the periphery of the rupturable metal sheet.
U.S. Pat. No. 4,498,261, referred to in the disclosure of the '632 patent, is a rectangular vent panel that opens under a relatively low pressure in which the thin sheet structure is described as being medium impact polystyrene, a relatively soft metal such as aluminum alloy, or a fully annealed stainless steel. Interrupted X-pattern slits extend through the vent panel and define individual lines of weakness that terminate at the apex of the X. A thin sealing membrane having the same area as the rupture panel is adhesively bonded to the rupture panel, and may be formed of polyethylene, stainless steel, or aluminum. Similar structure is shown and described in U.S. Pat. No. 4,612,739.
Although prior art pressure relief vents of the type described do satisfactorily open and relieve predetermined overpressure condition in protected spaces, these vents have remained open, thereby allowing the confined space to have continuing access to the surrounding atmosphere. Following outrush of products of combustion from the explosion or fire and relief of the high pressure, oxygen from the atmosphere is immediately available through the vent aperture that can produce a secondary explosion, exacerbation of a fire, or re-ignition of the fire.
More particularly, there has been a long-felt, but previously unfulfilled, requirement for vents that may be used with either rectangular or circular vent openings.